This invention relates to cables, in particular, to cables for electrical submersible pumps that are manufactured with electrically conductive layers formed coaxially around one or more of the primary conductor insulators to produce one or more capacitors integral to the cable.
Electrical submersible pump cables typically consist of a plurality of conductors wrapped with armor. Such cables have been used to transmit signals to equipment downhole. In some applications, armor around the cable has been used as a return path for a signal conductor. However, this method is not effective for use with very high frequency signals because the armor offers a high skin resistance as a return path. As a solution, an armored cable described in U.S. Pat. No. 3,916,685 has been implemented. However, the ""685 cable is not readily adaptable to tools designed for multiconductor cables. U.S. Pat. No. 4,028,660 teaches an armored multiconductor coaxial well logging cable for both high frequency signal and low frequency signal transmission in which a plurality of conductors form a shield for an inner conductor. The plurality of conductors are capacitively coupled so that each conductor group may carry a different low frequency signal or direct current voltage. The ""660 cable utilizes a coaxial conductor group, wherein each of the conductors within the group are separated from each other by an insulating material. A plurality of capacitors are connected between conductors within a coaxial conductor group. The multi-layer concentric conductors of the ""660 patent travel the full length of the cable on high voltage conductors. A signal is transmitted down an inner conductor and power is transmitted down an outer conductor.
Power cables for electrical submersible pumps have been used having an insulated conductor lead shield and wrapped with armor. Lead shields are not electrically insulated from armor or each other. The purpose of the lead shield is is to exclude hydrogen sulfide gas from contact with insulation of conductors.
The invention includes a specially modified electrical submersible pump cable or specially modified motor lead extension on the cable. The specially modified cable or section has a primary conductor and an insulator that surrounds the primary conductor. A coaxial conductive layer surrounds the insulator. The insulator serves as a dielectric between the primary conductor and the coaxial conductive layer. An outer insulating sleeve is provided on an outer surface of the coaxial conductive layer. An inner cable armor surrounds the insulating sleeve. The outer insulating sleeve provides electrical isolation between adjacent wires. An outer cable armor surrounds the inner cable armor.
The apparatus of the invention enables the coupling of data information onto or off of the primary conductor. Additionally, the invention enables coupling of data information onto or off of the coaxial conductive layer that surrounds the primary conductor. In a preferred embodiment, a motor lead extension is used to provide the capacitance necessary to couple the signal. The motor lead extension is typically 25-35 feet in length, although sufficient capacitance may be obtained in as little as twenty feet of the motor lead extension. The motor lead extension preferably has three conductors of copper surrounded by an insulation. The insulation is preferably polytetrafluoroethylene sold under the trademark TEFLON(copyright) for preventing shorting out between the conductors. Wires are inserted into the lead and into downhole instrumentation to transmit high frequency signals to the surface. A current modulator is used downhole to modulate the signal and to send data to the surface. Equipment at the surface monitors high and low frequencies to extract information from the signal. The signal may be routed up two or three phases of the cable. The information can be provided as a differential between two or three phases.